Carbanions Formation and Reactions Part 1 The CC
Carbanions: Formation and Reactions Part 1
The C-C bonds of a molecule under construction constitute its scaffolding. Reactions which form new C-C bonds are exceptionally useful synthetically. SN 2 reactions, which use a carbanion as a nucleophile represent one solution to this problem.
General Types of Carbanions
Formation of Stabilized Carbanions Note that, for this reaction to succeed, the carbanion must be a weaker base than the base employed to deprotonate its conjugate acid.
Increasing Basicity Bases often used to form (stabilized) carbanions
Formation of Alkynyl Anions (can be formed by deprotonation)
Alkynes
Reactions of Alkynyl Anions
Other Carbanions Formed by Deprotonation (Enolate Anions)
Grignard and Organolithium Species (Unstabilized Carbanions)
Formation of Organometallics by Reaction of Organohalides with Magnesium and Lithium Metal
Formation of Carbanions by Halogen -Metal Exchange Reactions This works when R’-M is a more stable organometallic (carbanion) than R-M. This reaction is often used to form vinyl- and aryl- carbanions, where the sp 2 hybridized orbital has more ‘s-character’ than the starting sp 3 hybridized orbital.
Formation of Organometallics by Halogen-Metal Exchange
Reactions of Organomagnesium and Organolithium Species
- Slides: 72
